The fact the morality was invented makes it synthetic but not necessarily relative. Numbers are also “made up”.
Its possible that moral truths are objective but our interpretation of these objective truths is imperfect and therefore seems relative.
To use another commenters example, the fact that killing is not morally blameworthy in some cases doesn’t mean that an absolute moral truth doesn’t exist but just that our concept of killing is just too broad to express it.
The fact the morality was invented makes it synthetic but not necessarily relative. Numbers are also “made up”.
Its possible that moral truths are objective but our interpretation of these objective truths is imperfect and therefore seems relative.
To use another commenters example, the fact that killing is not morally blameworthy in some cases doesn’t mean that an absolute moral truth doesn’t exist but just that our concept of killing is just too broad to express it.